i think that kids older then twelve shouldnt have to listen to there step parent because i have a step dad and he always has me do stuff that my mom asked him to do so i say no he also miss uses this advantage by throwing crap on my school bag and throwing paint on my $80 math book

Yes, children over the age of twelve should have to listen to their step-parents. The step parent, after the biological mother and/or father, is usually who custody of the child would go to were something to happen to the parents, providing the right legal process has been observed. Legal guardianship of the child would remain with the step parent until the child reaches the age of 18. A child should respect their step parent just as they would their biological parent or their grandparents.
Besides the "if" legal side of things, listening to your step parent would make life so much easier. No one wants to do everything that they're told to do, but it is a necessary skill in life to be able to follow directions and take orders. Just think of all of the disagreements that could be avoided if you swallowed your pride and just listened.